A vessel, vessel element, or vessel member is one of the cell types found in xylem. Xylem is the tissue in vascular plants which conducts water (and substances dissolved in it) upwards in a plant. In a live tree, vessels serve as the pipelines within the trunk, transporting sap within the tree. Conversely, softwoods completely lack vessels, and instead rely on tracheids for sap conduction. Vessel elements are the largest type of cells, and unlike the other hardwood cell types, they can be viewed individually—oftentimes even without any sort of magnification. Vessel elements are the building blocks of vessels, which constitute the major part of the water transporting system in those plants in which they occur. Vessels form an efficient system for transporting water (including necessary minerals) from the root to the leaves and other parts of the plant.
Cellulose pulps that contain hardwood pulp fibers that include vessels are used to produce consumer tissue or towel products. Consumer tissue and towel products made from these pulp fibers that offer both improved strength and increased softness are in increasing demand. However, the known strength/softness dynamic provides that as the tissue or towel product intrinsic strength increases, the overall softness decreases. In other words, the stronger you make a consumer tissue or towel product, the harder and more rigid (and the less soft) it becomes.
Further, as the world's supply of native softwood fibers become increasingly scarcer and more expensive, it has become necessary to consider lower cost, and more abundant, sources of cellulose to make paper products. This has caused a broader interest in papermaking with traditionally lower quality sources of fiber such as high lignin-content fibers and hardwood fibers, as well as fibers from recycled paper. Unfortunately, these sources of fiber often result in the comparatively severe deterioration of the strength characteristics of paper compared to conventional virgin chemical pulp furnishes.
Because of the above-mentioned reasons, pulps and processing methods of increasing the intrinsic sheet strength and the intrinsic sheet softness of consumer tissue and towel products produced by fibrous pulps are of great interest.
One method described herein can be used for the centrifugal separation of fibers having different apparent specific gravities (e.g., by classifying fibers by width). The resulting fractions can yield a pulp that can be used to produce a web product that has higher wet tensile and a higher overall softness than currently available products. In other words, it would be desirable to provide a cellulose pulp that produces a consumer relevant tissue or towel product that offers a higher level of wet tensile strength and a higher level of softness. Such a product would fly in the face of the known strength vs. softness dynamic and provide a consumer with a more enjoyable user experience.